1. Field of the Invention
This invention relates generally to optical encoders and more particularly to optical encoders utilized in connection with stepper motors which control high speed printers.
2. Description of the Prior Art
As is well known, carriage mounted print heads for dot matrix printers are controlled by stepper motors which in turn are controlled by a closed loop feedback systesm including a flat disk type of slotted code wheel or printed film strip having a source of light on one side of the disk and a photosensor on the other side for detecting the absence or presence of a slot or other indicia by the sensing of transmitted light between the emitter and sensor. Shaft position, direction and/or timing information in the form of an electrical pulse train is provided for controlling the stepper motor and accordingly the position of the print head.
While a rotational encoder utilized in connection with a stepper motor is disclosed in U.S. Pat. No. 4,289,983, entitled, "Encoder For Monitoring Bidirectional Motion", which issued to L. Bengner, et al. on Sept. 15, 1981, impact type printers utilizing such apparatus are additionally typically disclosed in the following references: U.S. Pat. No. 3,942,619, entitled, "Printer Employing Stylus Correlation and Motor Damping Means", which issued to L. Nordstrom, et al. on Mar. 9, 1976; U.S. Pat. No. 4,024,941, entitled, "Dot Matrix Type Serial Printer", which issued to A. Sekikawa, et al. on May 24, 1977; U.S. Pat. No. 4,376,585, entitled, "Combined Paper Advance and Ink Ribbon Feed System", which issued to L. Fromme, et al. on Mar. 15, 1983; U.S. Pat. No. 4,429,268, entitled, "Speed Control for Step Motors", which issued to T. Yajima, et al. on Jan. 31, 1984; and U.S. Pat. No. 4,465,959, entitled, "Step Motor Drive Control", which issued to T. Yajima on Aug. 14, 1984.
Accordingly, it is an object of the present invention to provide an improvement in electrically controlled printing apparatus.
It is another object of the invention to provide an improved optical encoder capable of sensing motor shaft position and direction as well as providing timing information for controlling a carriage mounted print head.
It is a further object of the invention to provide an improved optical encoder for printer control circuitry and which is adapted to provide reliable information while operating in a harsh environment.
And it is still a further object of the invention to provide an improved rotational encoder which is adapted to provide reliable and precise information as to motor shaft position and/or direction as well as timing information while operating in the presence of strong shock or vibration levels which ordinarily would curtail operation of electrically controlled dot matrix printers.